Development and validation of CAPS and AFLP markers for white rust resistance gene in<Emphasis Type="Italic"> Brassica juncea</Emphasis>

White rust, caused by Albugo candida, is a very serious disease in crucifers. In Indian mustard (Brassica juncea), it can cause a yield loss to the extent of 89.9%. The locus Ac2(t) controlling resistance to white rust in BEC-144, an exotic accession of mustard, was mapped using RAPD markers. In the present study, we developed: (1) a more tightly linked marker for the white rust resistance gene, using AFLP in conjunction with bulk segregant analysis, and (2) a PCR-based cleaved amplified polymorphic sequence (CAPS) marker for the closely linked RAPD marker, OPB06₁₀₀₀. The data obtained on 94 RILs revealed that the CAPS marker for OPB06₁₀₀₀ and the AFLP marker E-ACC/M-CAA₃₅₀ flank the Ac2(t) gene at 3.8 cM and 6.7 cM, respectively. Validation of the CAPS marker in two different F₂ populations of crosses Varuna × BEC-144 and Varuna × BEC-286 was also undertaken, which established its utility in marker-assisted selection (MAS) for white rust resistance. The use of both flanking markers in MAS would allow only 0.25% misclassification and thus provide greater efficiency to selection.Communicated by C. Möllers     

Identification and mapping of resistance gene analogs and a white rust resistance locus in<Emphasis Type="Italic"> Brassica rapa</Emphasis> ssp.<Emphasis Type="Italic"> oleifera</Emphasis>

The objective of this investigation was to tag a locus for white rust resistance in a Brassica rapa ssp. oleifera F₂ population segregating for this trait, using bulked segregant analysis with random amplified polymorphic DNA (RAPD) markers, linkage mapping and a candidate gene approach based on resistance gene analogs (RGAs). The resistance source was the Finnish line Bor4109. The reaction against white rust races 7a and 7v was scored in 20 seedlings from each self-pollinated F₂ individual. The proportion of resistant plants among these F₃ families varied from 0 to 67%. Bulked segregant analysis did not reveal any markers linked with resistance and, therefore, a linkage map with 81 markers was created. A locus that accounted for 18.4% of the variation in resistance to white rust was mapped to linkage group (LG) 2 near the RAPD marker Z19a. During the study, a bacterial resistance gene homologous to Arabidopsis RPS2 and six different RGAs were sequenced. RPS2 and five of the RGAs were mapped to linkage groups LG1, LG4 and LG9. Unfortunately, none of the RGAs could be shown to be associated with white rust resistance.Communicated by H.C. BeckerThe nucleotide sequence data reported has been deposited in the Genbank under the accession numbers AF315081–AF315087.     

Identification of RAPD markers linked to the Uvf-1 gene conferring hypersensitive resistance against rust (<Emphasis Type="Italic">Uromyces viciae-fabae</Emphasis>) in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

Bulk segregant analysis was used to identify random amplified polymorphic DNA (RAPD) markers linked to a gene determining hypersensitive resistance in Vicia faba line 2N52 against race 1 of the rust fungus Uromyces viciae-fabae. The monogenic nature of the resistance was determined by analyzing the F(2) population from a cross between resistant line 2N52 and susceptible line VF-176, and further confirmed in the F(2:3)-derived families. Linkage of the RAPD markers was confirmed by screening 55 F(2) plants segregating for resistance. Three RAPD markers (OPD13(736), OPL18(1032) and OPI20(900)) were mapped in coupling phase to the resistance gene for race 1 ( Uvf-1). No recombinants between OPI20(900) and Uvf-1 were detected. Two additional markers (OPP02(1172) and OPR07(930)) were linked to the gene in repulsion phase at a distance of 9.9 and 11.5 cM, respectively. The application of marker-assisted selection to develop new faba bean varieties with rust resistance genes is discussed.     

Genetic characterization and mapping of major gene resistance to potato leafroll virus in <Emphasis Type="Italic">Solanum</Emphasis><Emphasis Type="Italic">tuberosum</Emphasis> ssp. <Emphasis Type="Italic">andigena</Emphasis>

Major gene inheritance of resistance to Potato leafroll virus (PLRV) was demonstrated in a parthenogenic population derived from the highly resistant tetraploid andigena landrace, LOP-868. This major gene or chromosome region seems to control a single mechanism for resistance to infection and virus accumulation in this source. About 149 dihaploid lines segregated in a ratio of 107 resistant to 32 susceptible, fitting the expected ratio for inheritance of a duplex gene under random chromatid segregation. A tetraploid AFLP map was constructed using as reference the ultra high density (UHD) map. All AFLP markers associated with PLRV resistance mapped to the same linkage group. Map position was confirmed by analysis of previously-mapped SSR markers. Rl _adg is located on the upper arm of chromosome V, at 1 cM from its most closely linked AFLP marker, E35M48.192. This marker will be used to develop allele-specific primers or a pair of flanking PCR-based markers for their use in marker assisted selection.     

Identification and validation of RAPD and SCAR markers linked to the gene <Emphasis Type="Italic">Er3</Emphasis> conferring resistance to <Emphasis Type="Italic">Erysiphe pisi</Emphasis> DC in pea

Three genes, er1, er2 and Er3, conferring resistance to powdery mildew (Erysiphe pisi) in pea have been described so far. Because single gene-controlled resistance tends to be overcome by evolution of pathogen virulence, accumulation of several resistance genes into a single cultivar should enhance the durability of the resistance. Molecular markers linked to genes controlling resistance to E. pisi may facilitate gene pyramiding in pea breeding programs. Molecular markers linked to er1 and er2 are available. In the present study, molecular markers linked to Er3 have been obtained. A segregating F₂ population derived from the cross between a breeding line carrying the Er3 gene, and the susceptible cultivar ‘Messire’ was developed and genotyped. Bulk Segregant Analysis (BSA) was used to identify Random Amplified Polymorphic DNA (RAPD) markers linked to Er3. Four RAPD markers linked in coupling phase (OPW04_637, OPC04_640, OPF14_1103, and OPAH06_539) and two in repulsion phase (OPAB01_874 and OPAG05_1240), were identified. Two of these, flanking Er3, were converted to Sequence Characterized Amplified Region (SCAR) markers. The SCAR marker SCW4₆₃₇ co-segregated with the resistant gene, allowing the detection of all the resistant individuals. The SCAR marker SCAB1₈₇₄, in repulsion phase with Er3, was located at 2.8 cM from the gene and, in combination with SCW4₆₃₇, was capable to distinguish homozygous resistant individuals from heterozygous with a high efficiency. In addition, the validation for polymorphism in different genetic backgrounds and advanced breeding material confirmed the utility of both markers in marker-assisted selection.     

Genetic analysis and molecular mapping of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) stalk rot resistant gene<Emphasis Type="Italic"> Rfg</Emphasis>1

One single pathogen Fusarium graminearum Schw. was inoculated to maize inbred lines 1,145 (Resistant) and Y331 (Susceptive), and their progenies of F₁, F₂ and BC₁F₁ populations. Field statistical data revealed that all of the F₁ individuals were resistant to the disease and that the ratio of resistant plants to susceptive plants was 3:1 in the F₂ population, and 1:1 in the BC₁F₁ population. The results revealed that a single dominant gene controls the resistance to F. graminearum Schw.. The resistant gene to F. graminearum Schw. was denominated as Rfg1 according to the standard principle of the nomenclature of the plant disease resistant genes. RAPD (randomly amplified polymorphic DNA) combined with BSA (bulked segregant analysis) analysis was carried out in the developed F₂ and BC₁F₁ populations, respectively. Three RAPD products screened from the RAPD analysis with 820 Operon 10-mer primers showed the linkage relation with the resistant gene Rfg1. The three RAPD amplification products (OPD-20₁₀₀₀, OPA-04₁₁₀₀ and OPY-04₉₀₀) were cloned and their copy numbers were determined. The results indicated that only OPY-04₉₀₀ was a single-copy sequence. Then, OPY-04₉₀₀ was used as a probe to map the Rfg1 gene with a RIL F₇ mapping population provided by Henry Nguyen, which was developed from the cross S3×Mo17. Rfg1 was primarily mapped on chromosome 6 between the two linked markers OPY-04₉₀₀ and umc21 (Bin 6.04–6.05). In order to confirm the primary mapping result, 25 SSR (simple sequence repeat) markers and six RFLP (restriction fragment length polymorphism) markers in the Rfg1 gene-encompassing region were selected, and their linkage relation with Rfg1 was analyzed in our F₂ population. Results indicated that SSR marker mmc0241 and RFLP marker bnl3.03 are flanking the Rfg1 gene with a genetic distance of 3.0 cM and 2.0 cM, respectively. This is the first time to name and to map a single resistant gene of maize stalk rot through a single pathogen inoculation and molecular marker analysis.Communicated by H.F. Linskens     

Leaf gas exchange and chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence of <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> in response to <Emphasis Type="Italic">Puccinia psidii</Emphasis> infection

One of the most important diseases of eucalyptus plantations is caused by the rust fungus Puccinia psidii. While the genetic basis of rust resistance has been addressed recently, little is known about the physiological aspects of Eucalyptus–P. psidii interaction. In order to fill this gap, we undertook a study investigating the effects of P. psidii infection on photosynthetic processes of two E. urophylla clones with contrasting resistance to the pathogen. Our results show that gas exchange and chlorophyll a fluorescence parameters were virtually unaffected in the resistant clone. In the susceptible clone, photosynthetic rates were chiefly constrained by biochemical limitations to carbon fixation. Photosynthesis was impaired only in symptomatic tissues since the reductions in photosynthetic rates were proportional to the diseased leaf area. Rust infection provoked chronic photoinhibition to photosynthesis in the susceptible clone. Overall, differences in the ability for light capture, use and dissipation may play a significant role in explaining the clonal differences in Eucalyptus in response to P. psidii infection. To our knowledge, this is the first report of the effect of rust infection on gas exchange and chlorophyll a fluorescence parameters in Eucalyptus.     

Validation and identification of molecular markers linked to the leaf rust resistance gene <Emphasis Type="Italic">Lr</Emphasis>28 in wheat

Leaf rust resistance gene Lr28 controls one of the important resistances in the Indian subcontinent against the most prevalent Puccinia triticina pathotype 77-5. Pyramiding Lr28 with other resistance genes would therefore, provide durable resistance against rust, a process that can be facilitated by DNA markers. A microsatellite marker wmc313 linked to Lr28 at a distance of 5.0 cM was identified in the population HD2329 × HW2037. The marker was validated in another population developed from WL711× CS + Lr28: 2D/2M 3/8 (acc. 2956) as well as in a few near- isogenic lines (NILs) carrying gene Lr28. Compared to the previously reported marker TPSCAR SCS421₅₇₀, wmc313 is more closely linked to Lr28. Both these markers flanking the gene should be useful in the deployment of Lr28 into the breeding program using marker-assisted selection allowing pyramiding with other effective genes to confer durable resistance.     

Positioning of the major locus for <Emphasis Type="Italic">Puccinia psidii</Emphasis> rust resistance (<Emphasis Type="Italic">Ppr1</Emphasis>) on the <Emphasis Type="Italic">Eucalyptus</Emphasis> reference map and its validation across unrelated pedigrees

In this report the major locus for Puccinia psidii rust resistance, Ppr1, was positioned on the reference genetic map for Eucalyptus. Additionally, its position was validated by association genetics in a related and two unrelated pedigrees involving different Eucalyptus grandis resistant trees crossed to individuals of two other species, Eucalyptus tereticornis and Eucalyptus camaldulensis. These results are consistent with the hypothesis that Ppr1 controls a large proportion of the variation for rust resistance, strengthening its role as a major locus in Eucalyptus and providing its unequivocal genomic position on linkage group 3. A localized map with 19 microsatellite loci was built around Ppr1. Multiallelic profiles were observed at several mapped microsatellites suggesting recent tandem duplications in the genomic landscape surrounding Ppr1. Markers EMBRA125 and EMBRA1071 flank Ppr1 at 9.5% and 7% recombination, respectively, and were found to be in linkage equilibrium in a E. grandis breeding population, consistent with the expectations in outcrossed Eucalyptus. Their potential use for MAS will specifically be directed to identifying resistant offspring of P. psidii resistant parent trees that are heterozygous at Ppr1. In these circumstances, a significant amount of LD is expected to occur between specific alleles at flanking microsatellites and the resistance allele at Ppr1. Moreover, the positional information of Ppr1 paves the way for prospective undertakings in this genomic region with the upcoming availability of a draft genome for E. grandis.     

<Emphasis Type="Italic">Vr</Emphasis><Subscript><Emphasis Type="Italic">2</Emphasis></Subscript>: a new apple scab resistance gene

Reports from several European countries of the breakdown of the Vf resistance, the most frequently used source of resistance in breeding programs against apple scab, emphasize the urgency of diversifying the basis of apple scab resistance and pyramiding different apple scab resistances with the use of their associated molecular markers. GMAL 2473 is an apple scab resistant selection thought to carry the resistance gene Vr. We report the identification by BSA of three AFLP markers and one RAPD marker associated with the GMAL 2473 resistance gene. SSRs associated with the resistance gene were found by (1) identifying the linkage group carrying the apple scab resistance and (2) testing the SSRs previously mapped in the same region. One such SSR, CH02c02a, mapped on linkage group 2, co-segregates with the resistance gene. GMAL 2473 was tested with molecular markers associated with other apple scab resistance genes, and accessions carrying known apple scab resistance genes were tested with the SSR linked to the resistance gene found in GMAL 2473. The results indicate that GMAL 2473 does not carry Vr, and that a new apple scab resistance gene, named Vr ₂, has been identified.     

Fine genetic mapping of the <Emphasis Type="Italic">TuNI</Emphasis> locus causing systemic veinal necrosis by turnip mosaic virus infection in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

In the pathosystem of turnip mosaic virus (TuMV) and Arabidopsis thaliana, two distinct symptoms (mosaic symptom and veinal necrosis) were observed that were dependent upon the combination of the TuMV isolate and the Arabidopsis ecotype. The Col-0 ecotype developed mosaic symptoms after infection with the TuMV isolate Azu while the Ler ecotype developed veinal necrosis after infection with the same TuMV isolate. The Ler phenotype is controlled by a single dominant gene TuNI (TuMV necrosis inducer) which is located on chromosome 1. The TuNI gene was precisely mapped to the ~105 kb interval between the two markers of mXF41 and mRF28 by using several types of DNA polymorphism markers. Within this region, which included largely duplicated sequences, a total of 19 putative genes were predicted and 15 of these were classified into five gene families. The genes belonging to the gene families At1g58480 and At1g58602 may function in response to infection by pathogens. The gene family At1g58480 encodes lipase-like proteins, which might be involved in the induction of defence responses that are mediated by salicylic acid. The gene family At1g58602 encodes the CC-NBS-LRR (CNL) proteins, which are known to function as one of the plant resistance (R) proteins against pathogens. In the present study, the possibility that TuNI might function as an R gene was discussed.Y.K. and T.I. contributed equally to this study     

Development of sequence characterized DNA markers linked to leaf rust (<Emphasis Type="Italic">Hemileia vastatrix</Emphasis>) resistance in coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.)

Coffee leaf rust due to Hemileia vastatrix is one of the most serious diseases in Arabica coffee (Coffea arabica). A resistance gene (S_H3) has been transferred from C. liberica into C. arabica. The present work aimed at developing sequence-characterized genetic markers for leaf rust resistance. Linkage between markers and leaf rust resistance was tested by analysing two segregating populations, one F₂ population of 101 individuals and one backcross (BC₂) population of 43 individuals, derived from a cross between a susceptible and a SH3-introgressed resistant genotype. A total of ten sequence-characterized genetic markers closely associated with the S_H3 leaf rust resistance gene were generated. These included simple sequence repeats (SSR) markers, sequence-characterised amplified regions (SCAR) markers resulting from the conversion of amplified fragment length polymorphism (AFLP) markers previously identified and SCAR markers derived from end-sequences of bacterial artificial chromosome (BAC) clones. Those BAC clones were identified by screening of C. arabica genomic BAC library using a cloned AFLP-marker as probe. The markers we developed are easy and inexpensive to run, requiring one PCR step followed by gel separation. While three markers were linked in repulsion with the S_H3 gene, seven markers were clustered in coupling around the S_H3 gene. Notably, two markers appeared to co-segregate perfectly with the S_H3 gene in the two plant populations analyzed. These markers are suitable for marker-assisted selection for leaf rust resistance and to facilitate pyramiding of the S_H3 gene with other leaf rust resistance genes.     

Molecular mapping of the rust resistance gene <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">4</Emphasis></Subscript> to a large NBS-LRR cluster on linkage group 13 of sunflower

Rust is a serious fungal disease in the sunflower growing areas worldwide with increasing importance in North America in recent years. Several genes conferring resistance to rust have been identified in sunflower, but few of them have been genetically mapped and linked to molecular markers. The rust resistance gene R ₄ in the germplasm line HA-R3 was derived from an Argentinean open-pollinated variety and is still one of most effective genes. The objectives of this study were to determine the chromosome location of the R ₄ gene and the allelic relationship of R ₄ with the R _adv rust resistance gene. A total of 63 DNA markers previously mapped to linkage group (LG) 13 were used to screen for polymorphisms between two parental lines HA 89 and HA-R3. A genetic map of LG 13 was constructed with 21 markers, resulting in a total map length of 93.8 cM and an average distance of 4.5 cM between markers. Two markers, ZVG61 and ORS581, flanked the R ₄ gene at 2.1 and 0.8 cM, respectively, and were located on the lower end of LG 13 within a large NBS-LRR cluster identified previously. The PCR pattern generated by primer pair ZVG61 was unique in the HA-R3 line, compared to lines HA-R1, HA-R4, and HA-R5, which carry other R ₄ alleles. A SCAR marker linked to the rust resistance gene R _adv mapped to LG 13 at 13.9 cM from the R ₄ locus, indicating that R _adv is not an allele of the R ₄ locus. The markers tightly linked to the R ₄ gene will facilitate gene pyramiding for rust resistance breeding of sunflower.     

The development of ISSR-derived SCAR markers around the<Emphasis Type="Italic"> SEASONAL FLOWERING LOCUS</Emphasis> (<Emphasis Type="Italic">SFL</Emphasis>) in<Emphasis Type="Italic"> Fragaria vesca</Emphasis>

Fragaria vesca is a short-lived perennial with a seasonal-flowering habit. Seasonality of flowering is widespread in the Rosaceae and is also found in the majority of temperate polycarpic perennials. Genetic analysis has shown that seasonal flowering is controlled by a single gene in F. vesca, the SEASONAL FLOWERING LOCUS (SFL). Here, we report progress towards the marker-assisted selection and positional cloning of SFL, in which three ISSR markers linked to SFL were converted to locus-specific sequence-characterized amplified region (SCAR1–SCAR3) markers to allow large-scale screening of mapping progenies. We believe this is the first study describing the development of SCAR markers from ISSR profiles. The work also provides useful insight into the nature of polymorphisms generated by the ISSR marker system. Our results indicate that the ISSR polymorphisms originally detected were probably caused by point mutations in the positions targeted by primer anchors (causing differential PCR failure), by indels within the amplicon (leading to variation in amplicon size) and by internal sequence differences (leading to variation in DNA folding and so in band mobility). The cause of the original ISSR polymorphism was important in the selection of appropriate strategies for SCAR-marker development. The SCAR markers produced were mapped using a F. vesca f. vesca × F. vesca f. semperflorens testcross population. Marker SCAR2 was inseparable from the SFL, whereas SCAR1 mapped 3.0 cM to the north of the gene and SCAR3 1.7 cM to its south.Communicated by H. Nybom     

Characterization and fine mapping of <Emphasis Type="Italic">RppQ</Emphasis>, a resistance gene to southern corn rust in maize

Southern corn rust (SCR) is a fungal disease caused by Puccinia polysora Underw, which can infect maize and may result in substantial yield losses in maize production. The maize inbred line Qi319 carries the SCR resistance gene RppQ. In order to identify molecular markers linked to the RppQ gene, several techniques were utilized including random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP). In addition, sequence characterized amplified region (SCAR) techniques combined with bulked segregant analysis (BSA) were used. Seven RAPD markers, eight SSR markers, and sixty-three AFLP primer combinations amplified polymorphisms between two parents and two bulk populations. A large F₂ population was used for genetic analysis and for fine mapping of the RppQ gene region. One AFLP polymorphic band, M-CAA/E-AGC₃₂₄, was converted to a SCAR marker, MA7, which was mapped to a position 0.46 cM from RppQ. Finally, the RppQ gene was mapped between the SCAR marker MA7 and the AFLP marker M-CCG/E-AGA₁₅₇ with distances of 0.46 and 1.71 cM, respectively.     

Exploitation of colinear relationships between the genomes of<Emphasis Type="Italic"> Lotus japonicus</Emphasis>,<Emphasis Type="Italic"> Pisum sativum</Emphasis> and<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>, for positional cloning of a legume symbiosis gene

The Lotus japonicus LjSYM2 gene, and the Pisum sativum orthologue PsSYM19, are required for the formation of nitrogen-fixing root nodules and arbuscular mycorrhiza. Here we describe the map-based cloning procedure leading to the isolation of both genes. Marker information from a classical AFLP marker-screen in Lotus was integrated with a comparative genomics approach, utilizing Arabidopsis genome sequence information and the pea genetic map. A network of gene-based markers linked in all three species was identified, suggesting local colinearity in the region around LjSYM2/PsSYM19. The closest AFLP marker was located just over 200 kb from the LjSYM2 gene, the marker SHMT, which was converted from a marker on the pea map, was only 7.9 kb away. The LjSYM2/PsSYM19 region corresponds to two duplicated segments of the Arabidopsis chromosomes AtII and AtIV. Lotus homologues of Arabidopsis genes within these segments were mapped to three clusters on LjI, LjII and LjVI, suggesting that during evolution the genomic segment surrounding LjSYM2 has been subjected to duplication events. However, one marker, AUX-1, was identified based on colinearity between Lotus and Arabidopsis that mapped in physical proximity of the LjSym2 gene.Communicated by J.S. Heslop-Harrison     

New slow-rusting leaf rust and stripe rust resistance genes <Emphasis Type="Italic">Lr67</Emphasis> and <Emphasis Type="Italic">Yr46</Emphasis> in wheat are pleiotropic or closely linked

The common wheat genotype ‘RL6077’ was believed to carry the gene Lr34/Yr18 that confers slow-rusting adult plant resistance (APR) to leaf rust and stripe rust but located to a different chromosome through inter-chromosomal reciprocal translocation. However, haplotyping using the cloned Lr34/Yr18 diagnostic marker and the complete sequencing of the gene indicated Lr34/Yr18 is absent in RL6077. We crossed RL6077 with the susceptible parent ‘Avocet’ and developed F₃, F₄ and F₆ populations from photoperiod-insensitive F₃ lines that were segregating for resistance to leaf rust and stripe rust. The populations were characterized for leaf rust resistance at two Mexican sites, Cd. Obregon during the 2008–2009 and 2009–2010 crop seasons, and El Batan during 2009, and for stripe rust resistance at Toluca, a third Mexican site, during 2009. The F₃ population was also evaluated for stripe rust resistance at Cobbitty, Australia, during 2009. Most lines had correlated responses to leaf rust and stripe rust, indicating that either the same gene, or closely linked genes, confers resistance to both diseases. Molecular mapping using microsatellites led to the identification of five markers (Xgwm165, Xgwm192, Xcfd71, Xbarc98 and Xcfd23) on chromosome 4DL that are associated with this gene(s), with the closest markers being located at 0.4 cM. In a parallel study in Canada using a Thatcher × RL6077 F₃ population, the same leaf rust resistance gene was designated as Lr67 and mapped to the same chromosomal region. The pleiotropic, or closely linked, gene derived from RL6077 that conferred stripe rust resistance in this study was designated as Yr46. The slow-rusting gene(s) Lr67/Yr46 can be utilized in combination with other slow-rusting genes to develop high levels of durable APR to leaf rust and stripe rust in wheat.     

Molecular mapping of leaf rust resistance gene <Emphasis Type="Italic">Rph14</Emphasis> in <Emphasis Type="Italic">Hordeum vulgare</Emphasis>

An incompletely dominant gene conferring resistance to Puccinia hordei, Rph14, identified previously in an accession of Hordeum vulgare, confers resistance to all known pathotypes of P. hordei in Australia. Knowledge of the chromosomal location of Rph14 and the identification of DNA markers closely linked to it will facilitate combining it with other important leaf rust resistance genes to achieve long lasting resistance. The inheritance of Rph14 was confirmed using 146 and 106 F₃ lines derived from the crosses ‘Baudin’/‘PI 584760’ (Rph14) and ‘Ricardo’/‘PI 584760’ (Rph14), respectively. Bulk segregant analysis on DNA from the parental genotypes and resistant and susceptible DNA bulks using DArT markers located Rph14 to the short arm of chromosome 2H. DArT marker bPb-1664 was identified as having the closest genetic association with Rph14. PCR based marker analysis identified a single SSR marker, Bmag692, linked closely to Rph14 at a map distance of 2.1 and 3.8 cm in the ‘Baudin’/‘PI 584760’and ‘Ricardo’/‘PI 584760’ populations, respectively.     

Molecular mapping of a rust resistance gene <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">14</Emphasis></Subscript> in cultivated sunflower line PH 3

Sunflower, the fifth largest oilseed crop in the world, plays an important role in human diets. Recently, sunflower production in North America has suffered serious yield losses from newly evolved races of sunflower rust (Puccinia helianthi Schwein.). The rust resistance gene, designated R ₁₄ , in a germplasm line PH 3 originated from a wild Helianthus annuus L. population resistant to 11 rust races. PH 3 has seedling with an extraordinary purple hypocotyl color. The objectives of this study were to map both the R ₁₄ rust resistance gene and the purple hypocotyl gene-designated PHC in PH 3, and to identify molecular markers for marker-assisted breeding for sunflower rust resistance. A set of 517 mapped SSR/InDel and four SNP markers was used to detect polymorphisms between the parents. Fourteen markers covering a genetic distance of 17.0 cM on linkage group (LG) 11 were linked to R ₁₄ . R ₁₄ was mapped to the middle of the LG, with a dominant SNP marker NSA_000064 as the closest marker at a distance of 0.7 cM, and another codominant marker ORS542 linked at 3.5 cM proximally. One dominant marker ZVG53 was linked on the distal side at 6.9 cM. The PHC gene was also linked to R ₁₄ with a distance of 6.2 cM. Chi-squared analysis of the segregation ratios of R ₁₄ , PHC, and ten linked markers indicated a deviation from an expected 1:2:1 or 3:1 ratio. The closely linked molecular or morphological markers could facilitate sunflower rust-resistant breeding and accelerate the development of rust-resistant hybrids.     

High-resolution Mapping and Analysis of the Resistance Locus <Emphasis Type="Italic">Rpi-abpt</Emphasis> Against <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Potato

Introduction of more durable resistance against Phytophthora infestans causing late blight into the cultivated potato is of importance for sustainable agriculture. We identified a new monogenically inherited resistance locus that is localized on chromosome 4. The resistance is derived from an ABPT clone, which is originally a complex quadruple hybrid in which Solanum acaule, S. bulbocastanum, S. phureja and S. tuberosum were involved. Resistance data of the original resistant accessions of the wild species and analysis of mobility of AFLP markers linked to the resistance locus suggest that the resistance locus is originating from S. bulbocastanum. A population of 1383 genotypes was screened with two AFLP markers flanking the Rpi-abpt locus and 98 recombinants were identified. An accurate high-resolution map was constructed and the Rpi-abpt locus was localized in a 0.5 cM interval. One AFLP marker was found to co-segregate with the Rpi-abpt locus. Its DNA sequence was highly similar with sequences found on a tomato BAC containing several resistance gene analogues on chromosome 4 and its translated protein sequence appeared to be homologous to several disease resistance related proteins. The results indicated that the Rpi-abpt gene is a member of an R gene cluster.